I also feel that it is an authentication problem.
I work for a major university and I also see the problem occasionally with them. They (the university central IT folks) integrate their mail servers to authenticate to their central LDAP servers. When the LDAP servers are down users can't authenticate so it seems as though my password is wrong.
I'm not suggesting that JodoHost uses LDAP servers or anything like that. My guess would be that the usernames and passwords are stored locally on the mail server (is that correct) rather than in the PostgreSQL database server that runs H-Sphere (is that right?). But, something seems to get periodically out of whack. It doesn't seem to be a timeout issue, but an "access denied" type of issue.
I don't see it very often, by the way, but I do see it maybe once to four times per week.